Process for generating a pulse sequence

ABSTRACT

In order to simplify the process of plotting a pulse sequence controlling the course of an MR experiment, for example an NMR tomographic investigation, by which the excitation of an RF pulse bringing about transverse magnetization, the switching on and off of field gradients acting in different directions, superposed on a constant magnetic field, as well as the acquisition times, it is proposed to generate this pulse sequence by modification of standard pulse sequences and/or by composition from standard pulses. These pulses are offered on a picture screen (22) as simple symbols (42-49), icons, or brief designations for standard pulse sequences (36-41). By clicking-on of the offering fields, for example by means of a mouse (51), these elements can be copied on time axes (58) allocated to them and attached at the suitable release time point onto these axes. The pulse sequence thus determined is stored on-line. The input of parameters can occur by clicking-on of windows (57 and/or 61), into which the parameter values can be input. In an arrangement (10) suited for the execution of the process the icons (42-49) representing the standard pulses are arranged along an icon column (54) on the left image border of the picture screen (22), while standard pulse sequences (35-41) are recallable on a menu strip (56) along a &#34;horizontal&#34; border of the picture screen (22), represented by brief designations.

FIELD OF THE INVENTION

The invention relates to a method to generate a pulse sequenceeffecting, in an experiment or during an investigation based uponmagnetic resonance, e.g. NMR or ESR, a triggering of control signals atpredetermined times, by which physical quantities such as a polarizingmagnetic field H_(o), a carrier frequency, an amplitude and relativephase of an exciting electromagnetic RF field, gradient field generationin various coordinate directions, as well as detection times for theresponse signals resulting from the RF excitation of a sample orinvestigated object are controlled with respect to their sequence andtime dependence, whereby a set of parameters, which can be processed andstored in a computer, and changed by means of an input device dependingon the type of the experiment, is assigned to each of these physicalquantities, through which set the chronologically controlled retrievalof these parameters generates the control signal and whereby an imagesymbol which can be displayed on a screen of an input device for thedialogue of the user with the computer is allocated to each parameterset which generates a control signal if called and whereby a time markcan also be displayed on the screen. The invention is also concernedwith a device for carrying out this method.

BACKGROUND OF THE INVENTION

A method, for generating a pulse sequence as well as a device for itsexecution, is known from EP 0 287 661 A1. According to this publication,for example, the parameters: pulse shape, amplitude, and duration aswell as the temporal order of the pulses of the sequence are entered viathe input keyboard of the computer, and thereby the complete sequence isprogrammed.

Even though the generation of the pulse sequence is in principle simple,it appears to be, however, disadvantageous in the known method that theinput of the numerous parameters is complicated for the user because itis time-consuming.

The known process would still be afflicted with this disadvantage evenif, instead of a customary input keyboard, an arrangement further knownfrom EP 0 026 833 A2 should be used for the data input, offering to theuser a supply of parameters to be entered in the form of scalesallocated to these individually on a screen, on which scales, byshifting, e.g. mouse-controlled, of an arrow representation or rotationof a pointer representation, he can mark an input parameter value and/orlimit its range. The time expenditure required for a process modified insuch a manner for a complete data input would correspond, however, atleast to that which must be accepted by using the method known per sefrom EP 0287661 A1.

It is also known practice to define pulse sequences graphically by meansof a so-called light pen. This, too, although it appears to be "moregraphic" and thus simpler than an input of digital abstract values, iscomplicated and time-consuming inasmuch as, because of the stronglydiffering pulse durations of the control signals in the plotting of sucha sequence, the time scale of the "drawing" has to be changed veryfrequently.

A method of the type mentioned at the outset is finally known from IEEETransactions on Biomedical Engineering, vol. BME-34, No. 12, December1987; D. Foxvog et al.: "PUPA: A pulse programming assistant for NMRimaging", pages 938-942. Here, after the selection and possiblemodification of a pulse or of a pulse sequence, which is possible onlyby means of the input keyboard of the computer, the pulses or the pulsesequence are displayed on a screen, so that further requiredmodification is facilitated with the aid of the graphic representation.

SUMMARY OF THE INVENTION

The object of the invention is therefore to improve a method of the typementioned above such that the establishing of a sequence of controlsignals adapted to the experiment is considerably simplified for theuser, as well as to provide for a device to execute this improvedmethod.

This object is basically achieved with respect to the method byattaching the image symbol to the time mark and thus defining the pointin time at which said parameter set is retrieved to generate saidcorresponding control signals allocated to the physical quantity andthat the input and/or changing of a particular parameter set is effectedby opening at least one window on said screen allocated to at least oneof said image symbols corresponding to said particular parameter set andentering data into window fields of said window for the parameters ofsaid particular parameter set.

In an advantageous application and embodiment of this basic principlethe generation of the magnetic resonance pulse sequence is effected bychanging of standard pulse sequences whose parameter sets are stored inthe computer and which are retrievable and can be displayed on thescreen. It is preferred that generation of the magnetic resonance pulsesequence is effected by combining standard pulse sequences and/or byentering at least one additional standard pulse sequence into a standardpulse sequence which is predefined as being changeable.

By the possibility given according to the invention of composing aneeded sequence of control signals from elements prepared bysubprograms, for example by variation of standard pulse sequences whichare kept ready for frequently occurring types of experiments andinvestigation as offering and/or by putting together the pulse sequencefrom standard pulses of which also the standard pulse sequences (can)consist, the plotting of the needed sequence of control signals isconsiderably simplified. Programming operations in the sense of an inputof parameters are required only insofar as pulse sequences and/orelements of such offered with standard specifications still require anadaptation for the execution of the intended experiment.

Representation of the sequence of control signals is simplified by areduction of the number of time axes without impairing the completenessof the representation where in a display on the screen a common timeaxis is allocated to pulses which each control one of the physicalquantities via a common output channel; by displaying in a display ofthe total magnetic resonance pulse sequence only those pulses by animage symbol whose time sequence determines the course of the magneticresonance experiment; and thus "renouncing" the representation ofparameters which remain essentially constant during the experiment andby the "shortening" of the time axis needed for the representation whichmakes it possible to present the pulse sequences on a relatively largerscale whereby in a display of the total magnetic resonance pulsesequence time intervals where all control signals are constant are notdisplayed at full length but represented by representations of shortenedtime intervals such that the sequence of individual pulses is preservedwhereby the non-displayed time intervals are replaced by shorter windowsymbols, the corresponding windows containing the information about thelength of the non-displayed time interval.

With respect to the apparatus for performing the method according to theinvention, the object mentioned above is achieved by an apparatus forperforming the method with electronic control means which generatecontrol signals from stored parameter sets by means of a programmablecomputer, by which control signals functional components of theapparatus--transmitter, magnet, gradient system, and receiver means--canbe controlled in a sequence adapted to the purpose of an experiment or aroutine investigation in order to adjust the physical quantities,whereby, for the dialogue between on the one hand the computer (36),with its storage means, and on the other hand the user, retrieval andinput means are provided comprising a screen where image symbols (42through 49) can be displayed inside a symbol field (54), representing astore of standard pulses and/or sequences, whereby the time sequence ofstandard pulses and/or sequences can be determined by transfer of theimage symbols (42 through 49) onto time axes (58), representing controlchannels in the display on the screen and/or by shifting such symbolsalong the time axes, whereby the control signals represented by theimage symbols are generated and/or repeated if necessary after a startcommand, comprising control means (51,52) to shift a cursor (53) toselect individual image symbols (42 through 49) and to place them on thetime axes (58), and comprising input means (62) to specify thesymbolically represented pulses with respect to their characteristicparameters--e.g. pulse height, width, time profile of increasing anddecreasing slope.

In this apparatus the insertion of standard pulses into a standard pulsesequence to be altered and/or the arrangement of standard pulse symbolson time axes for the generation of a desired pulse sequence occurs bymeans of a curser. This shifting can be performed by means of the curserkeys of a usual input keyboard which is, however, in many respectscomplicated.

In contrast, by using a mouse or a joystick as control means to openwindows by clicking on the symbol field or an image symbol on a timeaxis which windows contain parameter fields which again can be clickedon to be inspected or to change parameters as well as control fieldswhich control the programming of the computer and the storing of thewindow parameters if clicked on, a further simplification of theselection of sequence elements and their arrangement on the time axes isachieved, whereby the use of a mouse also permits a "graphic" definitionof "special" pulse elements.

Combination of arranging image symbols representing standard pulses in a"vertical" image symbol column by using a symbol field which isrepresented as an image symbol column located along a vertical margin ofthe screen and where horizontal time axes are displayed within stripesoccupied by individual image symbol fields and using standard imagesymbols representing standard pulses or standard pulse sequences whichcan only be placed onto predetermined time axes and shifted along thesetime axes and restricting the standard image symbols so that they canonly be placed onto and/or shifted along one single time axis providesin a simple manner, safety means against "false programming".

A menue line can be displayed containing fields corresponding toindividual standard pulse sequences and, on clicking on one of thefields, the corresponding standard pulse sequence can be called to thescreen. This menue line for the selection of standard pulse sequencesfrom the screen can be supplemented by options whose selection andspecification define measures which are required for a large number ofpulse sequences, for example repetition of pulse sequences, breaking-offof the repetitions when a predeterminable signal-to-noise ratio isreached, as well as control of incremental changes of individual pulseparameters in successive reception cycles which are controlled by theparticular sequence of control signals.

Further details and features of the invention are apparent from thefollowing description of a special embodiment of the method according tothe invention and device for its execution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematically simplified block circuit diagram of adevice according to the invention in the particular form of an NMRspectrometer and

FIG. 2 shows a plot on a screen of a special sequence of control signalsin order t explain the function of the spectrometer according to FIG. 1and of a special embodiment of the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The magnetic resonance apparatus represented in FIG. 1 as a simplifiedblock circuit diagram, designated as a whole with 10, comprisesfunctional components which, with the functions explained below, areintended both for a nuclear magnetic resonance (NMR) spectrometer forscientific experiments, but can also be provided in an NMR tomographoperating with nuclear magnetic resonance, which is meant primarily forpurposes of medical diagnosis and, therefore, for rather routineexaminations.

The magnet always present in such MR systems 10, which generates aconstant magnetic field of high field strength and homogeneity to whicha sample or--in the case of tomography--parts of a human or animalorganism are exposed, is, in the interest of simplicity, not shown. Suchmagnets are today frequently constructed as cryomagnets withsuperconducting windings, which, once charged with a super-current whichgenerates a magnetic field of desired field strength, are maintainedover a relatively long time, for example a year, in the superconductingstate, without further intervention for control into the magnetic systemof issue here.

Only the functional components are represented with which experimentalquantities are fixed and/or varied during an experiment or aninvestigation with respect to their magnitude and time dependence. Theseare, embodied in electronic circuitry technique and functionalcombination known per se at least the following functional units:

1. A high-frequency (RF) transmitter 11, which generates a coherentelectric RF output signal with adjustable predeterminable frequency Ω₀.

2. A controllable power amplifier 12 connected to the output of the RFtransmitter 11,

3. A region 13, which may be called "investigation volume" in an NMRtomograph and "probe head" in an NMR spectrometer within which theinvestigated object can be permanently or temporarily subjected to thephysically influencing quantities relevant for the particular experimentor the intended investigation as for example, the following:

a) a quantitatively relatively slight increase or decrease of the fieldstrength of the magnetic field generated by the magnet of the NMR system10, whose direction defines the "longitudinal" direction of the magneticpolarization as the Z-direction in a cartesian coordinate system.

b) magnitudes, signs and periods of activity of field gradients Gz, Gxas well as Gy, which can be generated in the longitudinal Z-direction aswell as in the X and Y directions transverse thereto.

c) A first RF field which may be introduced by means of a transmittercoil (not shown) fed by the power amplifier 12, for the resonantexcitation of a transverse magnetization in a desired frequency range.

d) A second, likewise transverse RF field, by which in order to achievea decoupling of magnetic transitions of interest from interferingtransitions a saturation of a resonantly excitable magnetization statein a further frequency range is achievable.

4. A receiver device, designated as a whole with 18, comprising areceiver coil (not shown), a controllable preamplifier 14 and aphase-sensitive detector 16 connected to its output and a controllablephase shifter 17, with which the RF output signal of the RF transmitter(11) is fed to the phase-sensitive detector 16 as a reference signalsaid receiver arrangement, for example after termination of anexcitation of the transverse magnetization in the sample head 13generating electric output signals reflecting its change and decaycharacteristics from which, after processing and evaluation, accordingto known criteria, the information data determinable from the experimentor investigation can be recovered.

5. A pulse modulator 19 acting on the power amplifier 12, by means ofwhich the amplitudes of the output signal of the power amplifier 12driven with the carrier frequency Ω₀ of the RF transmitter 11 can bemodulated with a "square" or smoothly curved, for example a"bell-shaped" profile corresponding to a Gauss curve, given in the timedomain.

By this pulse modulation of the RF output signal of the power amplifier12, as seen in the frequency domain, the energy of the exciting RF fieldis distributed "on both sides of" the carrier frequency Ω₀ over a bandwidth that is greater the shorter the duration of the modulation pulse,where the amplitude distribution is determined within this band widthaccording to the Fourier theorem by the form of the modulation imposed,given in the time domain, or as known per se (DE-C 24 14 551).

6. A computer 21, which performs a Fourier transformation of the outputsignal of the phase sensitive detector 16 and generates an output whichis representable graphically as a frequency spectrum of the excitedresonance processes, for example by means of a monitor 22, or may bedocumented in other suitable manner, for example as a print-out.

7. An electric control arrangement designated as a whole with 23, whichemits control signals in a programmable sequence to a plurality ofoutputs allocated to the functional units 11,12,13,18,19 and 21explained above; by these control signals the functional units areactivated in a time sequence and duration determined by the pulsesequence for the onset of the physical quantities required for theparticular type of NMR experiment or investigation according to qualityand time correlation, to which also belong the detection time window ofthe receiver arrangement 18 as well as the activation time of thecomputer 21.

For the explanation of the electronic control arrangement 23, we nowrefer to the details in this 20 respect of FIG. 2, with the aid of whicha typical method is described which makes possible a simple programmingof the pulse sequences emitted by the outputs 24 to 35 of the controlarrangement 23.

It is assumed that it is sufficient to explain the control arrangement23 by its functions, whose realization is possible for a correspondinglytrained specialist who knows the purpose of the control arrangement 23by well known means of electronic circuit technology.

The control arrangement 23 comprises a programmable computer 36 with astorage unit in which standard pulse sequences 37 to 41 suited forvarious pulse NMR experiments are stored, which are convertible over anoutput mechanism represented by the outputs 24 to 35 of the computer 36into the control (voltage) signals required to drive the functionalunits 11,12,13,18 and 19 as well as 21 of the NMR arrangement. Thesestandard sequences are, as a rule, subcombinations of a set of standardpulses 42 to 49 as well as sequences of such pulses, from which thesequences are so to speak "composed". The pulse sequence coming into usefor a certain NMR experiment or also a tomographic investigation,requires in general an experiment-specific establishing of thecharacteristic parameters of its standard pulses, for example withrespect to pulse shape, pulse height and pulse duration, alteration ofone or more of these parameters in the course of successively followingtriggerings of the particular pulse sequence, etc. and thus a"programming" of its own.

The dialogue required in this respect between user and computer occursin the manner known from PC (personal computer) technology by means of amouse 51 or of a joy stick 52 which shift a cursor 53 on the screen 2onto image symbols that are allocated to the individual standard pulses,whereby these are selectable for input or for a change of theircharacteristic parameters. The image symbols allocated to the standardpulses 42 to 49 for which in the following the same reference signs areused as for the standard pulses 42 to 49, are represented according tothe representation of FIG. 2 on the left margin of the screen 23 in animage symbol column designated as a whole with 54.

Standard sequences 37 to 41 corresponding to various subcombinations ofstandard pulses 42 to 49 are reproduced in a menu strip running alongthe upper screen margin, designated as a whole with 56 by their usualbrief designations.

As examples for such standard pulses there are given:

The standard sequence 37--"FLASH" (fast low angle shot).

The standard sequence 38--"FISP" (fast imaging with steady precession)

The standard sequence 39--"CPMG" (Carr-Pucell-Meiboom-Gill sequence).

The standard sequence 40--"CYCLOPS" (quadrature phase cycling) and

The standard impulse sequence 41--"PAPS" (phase Alternating PulseSequence).

It is self-evident that the image symbols 42 to 49 or brief designationsof standard pulse sequences 37 to 41 given in the image symbol column 54and in the menu strip 56 of the screen representation according to FIG.2 are merely to be understood as examples and by no means as conclusive"listings" of the possible image symbols or standard pulse sequences.

Of the standard pulse sequences 37 to 41 cited in the menu strip 56 thefirst two--FLASH and FISP--are those of imaging in NMR tomography, whilethe three last-mentioned standard pulse sequences are for NMR pulseFourier spectroscopy.

In a typical procedure for the programming of the NMR arrangement 10 fora tomographic investigation, for example according to the FLASH process,the following procedure can be followed:

By approaching the field allocated to this standard pulse sequence 37 ofthe menu strip 56 with the pointer 53 of the mouse 51 and clicking-onthis field 37 there is opened a window designated as a whole with 57 onthe screen 22, which offers a graphic representation of the controlsignals used in this process. These control signals are reproducedinside the window 57 in the representation corresponding to the imagesymbols 42 to 49. They are reproduced there along "parallel" time axes58, which are allocated to the respectively used outputs of the computer36 of the control arrangement 23.

These are, according to the representation of FIG. 2, as seen from thetop downward, the output 25 for the drive signal of the pulse modulator19, the output 31 for the slice-selection gradient Gx, the output 30 forthe read gradient Gz, the output 32 for the phase encoding gradient Gy,the output 35 for the spoiler gradient 48 and the output 33 for theacquisition window 49.

In the representation of the pulse sequence 37, for the sake of clarity,time axes 58 and image symbols 42 and 45 to 49, representing theindividual pulses, are represented only insofar as necessary for theprogramming of the time sequence of the individual pulses, which can beeffected by shifting the image symbols 42 and 45 to 49 along their timeaxes 58 attaching to these by setting time marks 59, whereby it is, ofcourse, understood that time marks 59 arranged on top of each otherrepresent identical time points in the representation of the time axes58.

Output signals and their time dependencies, emitted at further outputs24, as well as 26 to 29 and 34 of the computer 36 can, if need be, berepresentable in one or more subwindow(s) 61 of the total representationwindow 57.

If need be, in the sub-window 61 further windows can be opened in whichby graphic symbols and/or data tables properties of the particularcontrol signal can be given. At times, such a sub-window 61 can occupythe entire screen depending on how complex the set of parameters iswhich specifies the particular control signal.

An input or change of the parameters characterizing a (standard) pulseof the pulse sequence occurs within the window 57 or 61 in which thisparameter is also recallable.

The input or change of parameters can occur graphically and/ornumerically, the latter through input of the numerical data via thekeyboard 62 of the computer 36.

In this regard, the "programming" of the excitation pulse 42 of thepulse sequence 37 occurs by clicking-on the image symbol 42 of the sametype in the image symbol column 54, whereupon the relevant image-symbolsub-window 61 is opened in which there are provided fields for the inputof its characteristic data, namely a field for 1. Pulse height, 2. Pulsewidth or duration, 3. Time point of the onset or time shift of the sameagainst a relevant time mark 59, 4. Carrier frequency Ω₀ of theexcitation RF as well as, 5. Pulse angle α about which the excitationpulse rotates the magnetization, and 6. relative phase of the pulse,with respect to the relevant reference frequency.

Other properties of an excitation pulse 42, the programming designationor input of which can be of importance for further NMR experimentsand/or investigations, are the functional purpose--for example to selectchemical shift or generate a representation range--as well as thefrequency and amplitude distribution of the properties determining theRF excitation spectrum such as pulse shape--for example Gauss shape 43or square shape 44 and, in particular in combination with the latter,pulse height and pulse width for the definition of the property "soft"or "hard".

In an analogous manner, the gradient pulses 45, 46 and 47 can berepresented graphically and/or by characteristic numerical data and beprogrammed by their acceptance or change. In this case also theblending-in of the time function of the rise of the gradient currentwith the possibility of observing the effect of the parameter changes onthe graphic respresentation is of special interest. When clicking-on theacquisition window pulse 49, in the allocated window 61, all data of thesignal reception are shown such as start and end of the signalacquisition, time parameters of the transmit-to-receive switching, thereception channels, the receiver phase, data of the filtering, of thespectral band width, as well as number and spacing of the digitalizationpoints for the received signals.

Sequences of control signals, however, can be programmed not only byinput or alteration of characteristic parameters for standard sequences37 to 41 already "offered" according to their basic type in the controlarrangement 23, but can also be generated by copying of the individualimage symbols 42 to 49 onto the time axis 58 in suitable numbers andcombinations, in which case establishing of the characteristicparameters in each case occurs again in the allocated windows 61 and, ifneed be, in subwindows, as already explained above. Likewise, fromstandard sequences 37 to 41 present in stock, partial sequences can becopied and inserted into an existing sequence and/or further pulses,available in the image symbol column 54, can be inserted into such astandard sequence and fixed to the suitable time marks on the time axes58. Here, standard sequences or partial sequences can also berepresented "abbreviated", i.e. essentially by a symbol that only showsits specific content by "clicking-on". Insofar as a pulse is notavailable in storage, it can be defined graphically and/or by input ofits numerical data and be stored as a quantity recallable by itself.

Properties of a sequence of control signals, such as, for example theirrepetition, which cannot be combined via image symbols and correspondingwindows can be "clicked on" on a separate, further menu strip (notrepresented) and quantified by input of corresponding data on windowfields allocated to these.

In sequences of control signals that are repeated quasi-periodically insuch a way that one or more of their pulse parameters are altered, thenumber of periodic repetitions required for the achievement of a certainsignal-to-noise ratio is fixed or established as desired by observingthe improvement in the signal-to-noise ratio on the monitor. The imagesymbol of the quantity that is changed, is expediently marked by coloror by a reversed representation. In a window allocated to the change,for example, a phase cycle or the increment of a gradient which is tochange in the course of a total investigation can be established.

It is also useful to emphasize pulses which are externally triggered bycolor or by reversed representation. Inside a window provided for thegeneration of parameters of such pulses, it is then specified that theshift with respect to a reference time mark (trigger) is variable.

For a compact representation of a sequence of control signals, it isuseful to shorten the time axes within the time intervals in which"nothing happens". The interval "removed" in such a manner from a timeaxis can be characterized by a small window with indication of theinterval duration, this interval duration, too, being variable byclicking-on the window and by entering the interval duration by means ofthe keyboard 62.

The computer 36 changes the progamming of the control arrangement 23either on-line or on closing of a window 57 or 61, or only afterconclusion of the generation of the total sequence. In this step, it isexamined whether the sequence can be realized by the hardware on hand,or whether it falls out of the framework of the usual or is evenassociated with danger to damage part of the apparatus 10. In the lastcase a warning and, under some circumstances, the refusal to convert thesequence, is given by the computer.

It is useful that the pulse sequence is documented together with themeasuring file, so that also in a later stage, the sequence linked to acertain measuring result can be reconstructed clearly and vividly.Moreover, provisions are taken that a pulse sequence generated in thisway and recognized as advantageous is completely stored and therebyadded to the stock of "standard pulse sequences".

We claim:
 1. An improved method for generating a magnetic resonancepulse sequence for the investigation of a sample by a magnetic resonanceexperiment, said method including the steps of triggering a controlsignal from electronic control means of a magnetic resonance apparatusat a predetermined time to generate a physical quantity havingindividual properties and a location in time with respect to a commonstarting point in time; setting in a programmable computer of themagnetic resonance apparatus a parameter set, having parameters,allocated to the physical quantity and to the control signal, theparameter set being processed and stored in the computer, and, during amagnetic resonance pulse sequence, a chronologically controlledretrieval of the parameter set generates the control signal; allocatingan image symbol to the parameter set, the image symbol being displayedon a screen of a computer monitor, and attaching a time mark to theimage symbol, the time mark also being displayed on the screen, theimprovement comprising:allocating a window to the image symbol; settingthe time mark to define a point in time at which the parameter setallocated to the control signal and to the physical quantity is to beretrieved; opening the window to input a particular parameter set, thewindow being on the screen; and entering data into a window field of thewindow for setting the parameters of a particular parameter set. 2.Method according to claim 1, characterized in that the parameter setallocated to the physical quantity comprises an amplitude and a relativephase of at least one rf pulse.
 3. Method according to claim 2,characterized in that the parameter set further comprises informationabout a typical shape of at least one rf pulse and in that the imagesymbol is allocated to that typical shape.
 4. Method according to claim3, characterized in that the parameter set further comprises informationabout a magnetic gradient field.
 5. Method according to claim 1,characterized in that the generation of the magnetic resonance pulsesequence is effected by changing a standard pulse sequence whoseparameter sets are stored in the computer and which are retrievable andcan be displayed on the screen.
 6. Method according to claim 5,characterized in that the generation of the magnetic resonance pulsesequence is effected by adding at least one additional standard pulsesequence to a standard pulse sequence which is predefined as changeable.7. Method according to claim 1, characterized in that, on a display onthe screen, a common time axis is allocated to pulses which each controlone of the physical quantities via a common output channel.
 8. Methodaccording to claim 1, characterized in that in a display of the totalmagnetic resonance pulse sequence only those pulses are displayed whichare represented by an image symbol whose time sequence determines thecourse of the magnetic resonance experiment.
 9. Method according toclaim 1, characterized in that in a display of the total magneticresonance pulse sequence on the screen, time intervals where all controlsignals which are constant are not displayed at a full length but arereplaced by shortened time intervals that preserve the sequence ofindividual pulses in the sequence, and the non-displayed time intervalsare replaced by windows containing information about the length of thenon-displayed time interval.
 10. An improved magnetic resonanceapparatus using a magnetic resonance pulse sequence for theinvestigation of a sample by a magnetic resonance experiment, saidmagnetic resonance apparatus including: electronic control means togenerate from parameter sets, having parameters, stored in aprogrammable computer, control signals for control channels, the controlsignals on said control channels controlling functional components ofthe magnetic resonance apparatus to generate and/or to change physicalquantities necessary for the magnetic resonance pulse sequence of themagnetic resonance experiment,the improvement comprising a screen whereimage symbols representing standard magnetic resonance pulses and/orstandard magnetic resonance pulse sequences for the generation and/orthe change of the physical quantities, can be displayed inside a symbolfield, and the time sequence of magnetic resonance standard pulsesand/or of standard magnetic resonance pulse sequences is determined bytransfer of the image symbols onto time axes on the screen representingcontrol channels or by shifting them along these time axes, and thecontrol signals generated from the stored parameters and represented bythe image symbols are generated and/or repeated after a start signal;control means to shift a cursor to select individual image symbols andto place them onto the time axes, and input means for inputtingproperties of magnetic resonance pulses and/or magnetic resonance pulsesequences to modify their parameter sets.
 11. Apparatus according toclaim 10, characterized by including a mouse or a joy stick as controlmeans to open windows by clicking on the symbol field or an image symbolon a time axis, the windows containing parameter fields which again canbe clicked on to be inspected or to change parameters as well as controlfields which control the programming of the computer and the storing ofthe parameters in the window if clicked on.
 12. Apparatus according toclaim 10, characterized by including a symbol field which is representedas an image symbol column located along a vertical margin of a screenand where horizontal time axes are displayed within stripes occupied byindividual image symbol fields.
 13. Apparatus according to claim 12,characterized by including standard image symbols representing standardpulses or standard pulse sequences which can only be placed ontopredetermined time axes and shifted along these time axes.
 14. Apparatusaccording to claim 13, characterized by including a standard imagesymbol which can only be placed onto or along one single time axis. 15.Apparatus according to claim 10, characterized by including a menu linewhich can be displayed containing fields corresponding to individualstandard pulse sequences and, when clicking on one of the fields, thecorresponding standard pulse sequence can be called to the screen.